Spain is famous for its weather, Benidorm, Spanish food, it's football team, Barcelona, and basically being a rather sunny place overall â none of these descriptions are incorrect, and in fact they are all entirely true!
As the temperature of the air increases its density decreases. Therefore the thrust produced by the engine decreases. As the air pressure increases, its density increases, causing thrust produced by the engine to increase. Altitude has a double effect on thrust. As the altitude increases, the air becomes colder and denser, up to the beginning of stratosphere. This causes the thrust to increase.
Thrust is a reaction force described quantitatively by Isaac Newton's second and third laws. When a system expels or accelerates mass in one direction, the accelerated mass will cause a force of equal magnitude but opposite direction on that system. The force applied on a surface in a direction perpendicular or normal to the surface is called thrust.